Kelch-like proteins in the gastrointestinal tumors.

Gastrointestinal tumors have become a worldwide health problem with high morbidity and poor clinical outcomes. Chemotherapy and surgery, the main treatment methods, are still far from meeting the treatment needs of patients, and targeted therapy is in urgent need of development. Recently, emerging evidence suggests that kelch-like (KLHL) proteins play essential roles in maintaining proteostasis and are involved in the progression of various cancers, functioning as adaptors in the E3 ligase complex and promoting the specific degradation of substrates. Therefore, KLHL proteins should be taken into consideration for targeted therapy strategy discovery. This review summarizes the current knowledge of KLHL proteins in gastrointestinal tumors and discusses the potential of KLHL proteins as potential drug targets and prognostic biomarkers.

Arctigenin impairs UBC12 enzyme activity and cullin neddylation to attenuate cancer cells.

Neddylation is a type of posttranslational protein modification that has been observed to be overactivated in various cancers. UBC12 is one of two key E2 enzymes in the neddylation pathway. Reports indicate that UBC12 deficiency may suppress lung cancer cells, such that UBC12 could play an important role in tumor progression. However, systematic studies regarding the expression profile of UBC12 in cancers and its relationship to cancer prognosis are lacking. In this study, we comprehensively analyzed UBC12 expression in diverse cancer types and found that UBC12 is markedly overexpressed in most cancers (17/21), a symptom that negatively correlates with the survival rates of cancer patients, including gastric cancer. These results demonstrate the suitability of UBC12 as a potential target for cancer treatment. Currently, no effective inhibitor targeting UBC12 has been discovered. We screened a natural product library and found, for the first time, that arctigenin has been shown to significantly inhibit UBC12 enzyme activity and cullin neddylation. The inhibition of UBC12 enzyme activity was newly found to contribute to the effects of arctigenin on suppressing the malignant phenotypes of cancer cells. Furthermore, we performed proteomics analysis and found that arctigenin intervened with cullin downstream signaling pathways and substrates, such as the tumor suppressor PDCD4. In summary, these results demonstrate the importance of UBC12 as a potential therapeutic target for cancer treatment, and, for the first time, the suitability of arctigenin as a potential compound targeting UBC12 enzyme activity. Thus, these findings provide a new strategy for inhibiting neddylation-overactivated cancers.

Targeting Cul3-scaffold E3 ligase complex via KLHL substrate adaptors for cancer therapy.

Targeted therapy has become increasingly important and indispensable in cancer therapy. Cullin3-RING ligases (CRL3) serve as essential executors for regulating protein homeostasis in cancer development, highlighting that CRL3 might be promising targets in various cancer treatment. However, how to design new targeted therapies by disrupting the function of CRL3 is poorly understood. Here, we focus on the substrate adaptors of CRL3, and carry out a systematical research on the function of Kelch-like (KLHL) family proteins. We have identified twenty-four KLHL proteins with function of tumor promotion and thirteen KLHL proteins with high clinical significance on cancer therapy. Furthermore, we have clarified the novel biological function of KLHL13 as a vital factor that contributes to malignant progression in lung cancer. Taken together, our findings reveal multiple potential therapeutical targets and provide evidence for targeting CRL3 via KLHL substrate adaptors for cancer therapy.

Ubiquitin-dependent degradation of CDK2 drives the therapeutic differentiation of AML by targeting PRDX2.

A distinct hallmark of acute myeloid leukemia (AML) is the arrest of leukemic myeloblasts at an immature stage of development. Therapies that overcome differentiation arrest have emerged as a powerful strategy for treating AML, but targeting leukemia differentiation remains challenging, mainly because of an incomplete mechanistic understanding of the process. Here, we unveil a new role for cyclin-dependent kinase 2 (CDK2) in blocking myeloid differentiation in AML. We show that among several interphase CDK, only CDK2 undergoes ubiquitin-dependent proteasome degradation, which is accompanied by AML cell differentiation. By using the yeast 2-hybrid system and functional analyses, KLHL6 was identified as a specific E3 ubiquitin ligase regulating the degradation of CDK2. Importantly, inhibiting CDK2, but not other cyclin-dependent kinases CDK1/4/6, effectively induced granulocytic differentiation in AML cell lines and 5 major subtypes of primary patient-derived AML samples. Mechanistically, CDK2 depletion led to the reactivation of differentiation pathway translation, and the differentiation blockade function of CDK2 may be achieved directly by maintaining the activity of PRDX2. Finally, CDK2 depletion arrested tumor growth of AML cells in nude mice and extended survival in both AML cell line and PDX-AML cells derived xenograft mouse models. Thus, our work not only provides experimental evidence for validating CDK2 as a potential therapeutic target for differentiation, but also uncovers the biological function of the CDK2-PRDX2 axis in blocking AML differentiation.

CDK2 suppression synergizes with all-trans-retinoic acid to overcome the myeloid differentiation blockade of AML cells.

A characteristic feature of leukemia cells is a blockade of differentiation in cellular maturation. All-trans-retinoic acid (ATRA) has been successfully applied for the treatment of M3-type AML (APL, 10 %), but it fails to demonstrate a significant efficacy on the remaining patients with non-APL AML (90 %). Therefore, the research for strategies to extend the efficacy of ATRA-based therapy to non-APL AML is a key avenue of investigation. Here, we evaluate the synergetic effect of CDK2 inhibition and ATRA in AML both in vitro and in vivo. We have determined that both the CDK2 depletion and pharmacological inhibitor of CDK2 significantly sensitize three subtypes of AML cells (including two non-APL cells) to ATRA-induced cell differentiation. RNA-sequence results indicate that transcription activation of differentiation and maturation pathways plays an important role in this synergetic effect. Furthermore, the down-regulation of CDK2 sensitized AML cells to ATRA-induced engraftment prevention of leukemia cells in NOD-SCID mice and promotes the primary AML blasts differentiation when combined with ATRA. Thus, our work not only provides relevant experimental evidence for further validating CDK2 as a target for differentiation therapy, but also uncovers the future clinical application of CDK2 inhibitors in ATRA-based differentiation therapeutics for AML.

Kelch-like proteins: Physiological functions and relationships with diseases.

Kelch-like gene family members (KLHLs) encode proteins with a bric-a-brac, tramtrack, broad complex (BTB)/poxvirus and zinc finger (POZ) domain, a BACK domain, and six Kelch motifs, which frequently interact with Cullin3 to form E3 ligase complexes that mediate the ubiquitination of substrate proteins. In recent years, studies have revealed that mutations and abnormal expression of KLHLs are closely related to the pathogenesis of various human diseases. Increasing evidence has shown that Kelch-like protein family members (KLHLs) exert important biological functions through the ubiquitination of specific substrates. This review provides an overview of the identified substrates of different KLHLs, summarizes the current knowledge of KLHLs and discusses the biological functions of KLHLs in different diseases.

Inhibition of M2-like macrophages by all-trans retinoic acid prevents cancer initiation and stemness in osteosarcoma cells.

Emerging evidence indicates that M2-polarized tumor-associated macrophages (TAMs) directly participate in tumor initiation, progression and metastasis. However, to date, few studies have investigated novel strategies for inhibiting TAMs in order to overcome osteosarcoma. In this study, we reported that M2 macrophages were enriched in osteosarcoma tissues from patients, and M2-polarized TAMs enhanced cancer initiation and stemness of osteosarcoma cells, thereby establishing M2-polarized TAMs as a therapeutic target for blocking osteosarcoma formation. We also found that all-trans retinoic acid (ATRA) weakened TAM-induced osteosarcoma tumor formation by inhibiting M2 polarization of TAMs in vivo, and inhibited the colony formation, as well as sphere-formation capacity of osteosarcoma cells promoted by M2-type macrophages in vitro. Furthermore, M2-type macrophages enhanced cancer stem cells (CSCs) properties as assessed by increasing the numbers of CD117+Stro-1+ cells accompanied by the upregulation of CSC markers (CD133, CXCR4, Nanog, and Oct4), which could clearly be reduced by ATRA. Taken together, the results of this study demonstrated the role of M2-polarized TAMs in osteosarcoma initiation and stemness by activating CSCs, and indicated that ATRA treatment is a promising approach for treating osteosarcoma by preventing M2 polarization of TAMs.

AKT inhibitor Hu7691 induces differentiation of neuroblastoma cells.

While neuroblastoma accounts for 15% of childhood tumor-related deaths, treatments against neuroblastoma remain scarce and mainly consist of cytotoxic chemotherapeutic drugs. Currently, maintenance therapy of differentiation induction is the standard of care for neuroblastoma patients in clinical, especially high-risk patients. However, differentiation therapy is not used as a first-line treatment for neuroblastoma due to low efficacy, unclear mechanism, and few drug options. Through compound library screening, we accidently found the potential differentiation-inducing effect of AKT inhibitor Hu7691. The protein kinase B (AKT) pathway is an important signaling pathway for regulating tumorigenesis and neural differentiation, yet the relation between the AKT pathway and neuroblastoma differentiation remains unclear. Here, we reveal the anti-proliferation and neurogenesis effect of Hu7691 on multiple neuroblastoma cell lines. Further evidence including neurites outgrowth, cell cycle arrest, and differentiation mRNA marker clarified the differentiation-inducing effect of Hu7691. Meanwhile, with the introduction of other AKT inhibitors, it is now clear that multiple AKT inhibitors can induce neuroblastoma differentiation. Furthermore, silencing AKT was found to have the effect of inducing neuroblastoma differentiation. Finally, confirmation of the therapeutic effects of Hu7691 is dependent on inducing differentiation in vivo, suggesting that Hu7691 is a potential molecule against neuroblastoma. Through this study, we not only define the key role of AKT in the progression of neuroblastoma differentiation but also provide potential drugs and key targets for the application of differentiation therapies for neuroblastoma clinically.

FAT10: Function and Relationship with Cancer.

Posttranslational protein modifications are known to be extensively involved in cancer, and a growing number of studies have revealed that the ubiquitin-like modifier FAT10 is directly involved in cancer development. FAT10 was found to be highly upregulated in various cancer types, such as glioma, hepatocellular carcinoma, breast cancer and gastrointestinal cancer. Protein FAT10ylation and interactions with FAT10 lead to the functional change of proteins, including proteasomal degradation, subcellular delocalization and stabilization, eventually having significant effects on cancer cell proliferation, invasion, metastasis and even tumorigenesis. In this review, we summarized the current knowledge on FAT10 and discussed its biological functions in cancer, as well as potential therapeutic strategies based on the FAT10 pathway.

All-Trans Retinoic Acid Prevents Osteosarcoma Metastasis by Inhibiting M2 Polarization of Tumor-Associated Macrophages.

M2-polarized tumor-associated macrophages (TAM) play a critical role in cancer invasion and metastasis. Here, we report that M2 macrophages enhanced metastasis of K7M2 WT osteosarcoma cells to the lungs in mice, thus establishing M2 TAMs as a therapeutic target for blocking osteosarcoma metastasis. We found that all-trans retinoic acid (ATRA) inhibited osteosarcoma metastasis via inhibiting the M2 polarization of TAMs. ATRA suppressed IL13- or IL4-induced M2-type macrophages, and then inhibited migration of osteosarcoma cells as promoted by M2-type macrophages in vitro ATRA reduced the number of pulmonary metastatic nodes of osteosarcoma and decreased expression of M2-type macrophages in metastatic nodes both in intravenous injection and orthotopic transplantation models. ATRA's effect was independent of conventional STAT3/6 or C/EBPß signaling, which regulate M2-like polarization of macrophages. Quantitative genomic and functional analyses revealed that MMP12, a macrophage-secreted elastase, was elevated in IL13-skewed TAM polarization, whereas ATRA treatment downregulated IL13-induced secretion of MMP12. This downregulation correlates with the antimetastasis effect of ATRA. Our results show the role of TAM polarization in osteosarcoma metastasis, identify a therapeutic opportunity for antimetastasis treatment, and indicate ATRA treatment as an approach for preventing osteosarcoma metastasis via M2-type polarization intervention. Cancer Immunol Res; 5(7); 547-59. ©2017 AACR.